A number of line grip devices have been invented and patented which are designed to travel up and down a vertical safety line and clamp onto the line so as to prevent the object from falling when pressure is exerted on the handle of the device. Dodge Machine Co., Inc. currently offers a rope grip for a vertical line with a number of desirable qualities, for example the rope grip is manufactured from large simple pieces of material which distribute the impact of a fall through relatively massive pieces of metal providing for strength, reliability, and safety. It can be attached to a person by means of a lanyard so that it can be moved up and down the rope without the person having to place his hand on the grip which makes it convenient to use. This rope grip can be placed over a rope anywhere along the length of a rope, providing additional convenience. The Dodge rope grip is versatile as it can be used with ropes having a variation in diameter of as much as a quarter of an inch. A patent application for this device is now pending, entitled "Removable Double Action Rope Grip" , U.S. Ser. No. 501,623 now U.S. Pat. No. 4,502,668.
Another such device is the Barrow-Hepburn Everest Rope Grip patented in the U.K. as Pat. No. 1,077,068. This rope grip operates by means of three steel balls in a conical housing. The rope is passed through the steel balls so that when the grip begins to fall rapidly down the rope the steel balls are drawn into the conical housing, jamming the rope. This rope grip thus provides a degree of fail safe operation in vertical line grips.
The prior art has serious shortcomings with respect to providing effective means for protecting a worker who depends upon a horizontal safety line. In many ways a horizontal safety line provides optimal protection for a worker on a scaffold. This is so because a scaffold worker needs adequate freedom of movement particularly in a horizontal direction. In order to have the necessary freedom of movement, there would have to be a considerable amount of slack in any type of vertical safety line. Accordingly, in the event of a failure of a support line of the scaffolding a worker would fall a considerable distance before a vertical safety line would take effect; whatever gripping device was used.
If one of the supporting lines of the scaffold fails, thus suddenly causing that end of the scaffold to fall downward, a worker should be protected by a horizontal line. Such a horizontal line could be mounted on the scaffold. A horizontal line gripping device suitable for use on this type of horizontal line must be able to clamp onto the line as a result of rapid movement in either direction. The prior art does not meet this need.
Because of the law of gravity discovered by Newton, that objects having different weights will all fall at the same rate of speed, it is advantageous for a line grip device to employ means which will actuate the device when upward pressure is removed. Prior inventions describe a great number of different types of springs arrangements which can be used to activate line grip devices when upward pressure is removed. In the case of a line grip device operating on a horizontal line, it is not practical to have the device operated by means of a spring which is counteracting the gravitational weight of the device. The present invention solves this problem by using the spring action of the line on which the device is mounted to actuate the device. In this way the device will actuate in two directions rather than in one as is the case with a multiplicity of vertical devices.